In medical imaging (e.g., imaging body cavities or organs) and optical neuromodulation, it can be desirable to pinpoint the locations of the interactions between light and biological tissues at multiple sites with precise spatial and temporal control.
Conventional techniques in medical imaging usually rely on scanning confocal microscopy or fiber optics (e.g., in endoscopy). In confocal microscopy, the penetration depth can be limited by scattering and absorption in tissues. In fiber optics, scaling the number of accessible interaction sites typically involves increasing the number of fibers in a bundle. The resulting large footprint and mechanical rigidity of fiber bundles may preclude their applications in delicate tissues such as human inner ear and brain. For example, state-of-the-art endoscopes can have relatively large sizes (around 1 mm in diameter or larger) and limited structural flexibility, making it difficult to image delicate organs or tissues. Further, most endoscopes have a small field of view since they acquire images through the end opening of the endoscope.
On the other hand, optical stimulation of biological tissues (e.g. neurons) involves the inverse problem of optical imaging. At present, optogenetic neuromodulation is predominantly performed using optical fiber probes. In general, a single optical fiber probe permits optical stimulation at one spatial site. Multi-site stimulation and modulation usually uses fiber bundles or waveguide arrays. These solutions can drastically increases the probe size, mechanical rigidity, and hence invasiveness to biological tissues.
Fiber probes structured with focused ion beams may be employed for spatially addressed optogenetic stimulation, but the approach includes complicated nanofabrication and may not be scalable to high-density neural stimulation. In addition, the approach usually suffers from excessive optical loss due to the metal coating and circular symmetry of the fiber. Flexible light emitting diode (LED) arrays may be an alternative to fiber optic neural probes. However, heat generation from the LED devices can easily lead to thermal damage to fragile neural tissues. Consequently, these “active” approaches, which use the integration of active optoelectronic LED devices on the probe, are generally not preferred for optogenetic applications.